SAN FERNANDO, Mexico — Working under heavy security in a region controlled by a brutal drug gang, authorities and diplomats began the gruesome task Thursday of identifying 72 Central and South American migrants killed just 100 miles from their destination — the U.S. border. Marines guarded the pink, one-story funeral home where the bodies were taken after being discovered on a ranch Tuesday, bound, blindfolded and slumped against a wall. A funeral home employee, who like most people in San Fernando was too frightened to give his name, said the dead were stored in a refrigerated truck in the parking lot, where flies buzzed over white powder spread over bloodstains. The victims of what could be Mexico's biggest drug-gang massacre were trying to reach Texas, traversing some of Mexico's most dangerous territory. The lone survivor said the assassins identified themselves as Zetas, a drug gang that dominates parts of the northern state of Tamaulipas. "This is frightening. It's horrible," said a tortilla stand worker in San Fernando, a crumbling colonial town of about 30,000 people on Mexico's east coast. "It smells like death. I vomited," his friend added. Tamaulipas state Assistant Attorney General Jesus de la Garza told the Milenio television network that 15 bodies had been identified. De la Garza said eight were from Honduras, four from El Salvador, two from Guatemala and one from Brazil. Diplomats from Brazil, Ecuador, El Salvador and Honduras arrived or were en route to help identify the bodies. "We have firmly asked the Mexican authorities to conduct an exhaustive investigation to find those responsible for this abominable event," Salvadoran Foreign Minister Hugo Martinez said. Mexico's National Human Rights Commission sent investigators to monitor the identification process. Marines discovered the horrific massacre after the survivor, 18-year-old Luis Freddy Lala Pomavilla of Ecuador, staggered wounded to a military checkpoint.